The purpose of this research is an analysis of the behavioral endocrinology of mammalian social behavior. This research will focus on unique animal models for the analysis of neurochemical factors associated with the development and expression of social behavior and monogamy. The species to be studied in detail is the native American rodent, the prairie vole, Microtus ochrogaster captured in Illinois (which is highly social and monogamous). Monogamy in voles, and other mammals, is characterized by reduced sexual dimorphism in adulthood, male-female pairbonding, male parental care, and vulnerability of both sexes to reproductive suppression within a family group. We have demonstrated a role for centrally active oxytocin in social behavior and pair bond formation in prairie voles, and will continue to analyze the neural mechanisms responsible for oxytocin's behavioral action. In addition, prairie voles exhibit exceptionally high levels of glucocorticoids and glucocorticoid resistance. We propose to test the hypothesis that high levels of corticosterone during development, may create a form of natural "perinatal stress", which in turn "demasculinizes" male prairie voles, accounting for reduced sexual dimorphism, male parental care and vulnerability to reproductive inhibition. We plan to study montane voles (microtus montanus) and a population of prairie voles from a drier habitat (which are apparently less social, more aggressive and not monogamous) to test hypotheses regarding physiological mechanisms responsible for monogamy and high levels of social behavior from a comparative and genetic perspective. There is great value in understanding the behavioral effects of hormones such as oxytocin and the hormones of the adrenal axis (which are widely used in medicine).